The invention relates generally to subcritical vapor compression systems that use expansion devices to control compressor suction superheat and, more particularly, to a method and apparatus for determining refrigerant charge adequacy in an air conditioning system.
Maintaining proper refrigerant charge level is essential to the reliable and efficient operation of an air conditioning system. Improper charge level, either in deficit or in excess, can cause premature compressor failure. An over-charge in the system results in compressor flooding, which, in turn, may be damaging to the motor and mechanical components. Inadequate refrigerant charge can lead to increased power consumption, thus reducing system capacity and efficiency. Low charge also causes an increase in refrigerant temperature entering the compressor, which may cause thermal overload of the compressor. Thermal overload of the compressor can cause degradation of the motor winding insulation, thereby bringing about premature motor failure.
The traditional techniques for assessing the charge level are the superheat method for fixed-orifice systems and the subcool method for systems equipped with an expansion valve. Normally, a service technician performs refrigerant charge assessments manually using pressure gauge(s) and temperature meter(s). In an automated type sensor, both techniques require a pressure transducer to measure the pressure and ultimately the saturation temperature of the refrigerant at some point in the circuit. Pressure transducers are undesirable due to relative high cost and must be inserted in the circuit which can cause pressure drops and potential leaks.